Rechargeable lithium-ion batteries are characterized by high specific energy and power. They are therefore preferably used in applications which require the smallest possible weight and little space. Thus, it is lithium-ion secondary batteries that are predominantly used today as energy stores for portable electronic devices, such as e.g. video cameras, laptop computers or mobile phones. If the production costs of rechargeable lithium batteries are further reduced, further potential applications are conceivable, such as e.g. cordless power tools, onboard power supply, traction or hybrid batteries in vehicles, or also in stationary applications, e.g. for emergency power supply equipment.
The operating principle of current lithium-ion batteries is based on the use of electrode materials which can intercalate lithium reversibly. At present, carbon compounds are customarily used as anode and a lithium-containing oxide as cathode.
In order to be able to obtain the highest possible energy densities, cathode materials which can intercalate lithium at potentials between 3 and 4 V vs. Li/Li+ are preferably used. The most promising materials which meet these requirements include lithium compounds based on cobalt, nickel, iron and manganese oxides. For reasons of cost and because they are more environmentally friendly and safer to use, manganese- and iron-based materials are currently preferred.
Of the lithium manganese oxides, compounds with spinel structure, such as e.g. LiMn2O4 (stoichiometric spinel), Li2Mn4O9 (oxygen-rich spinel) and Li4Mn5O12 (lithium-rich spinel), show the most promising properties as cathode materials. Normally, these spinels are prepared by means of solid-state reactions. This normally results in stoichiometric spinels which, however, in most cases have only an inadequate cycle life. This is attributed to changes and defects in the lattice structure which occur during the insertion and removal of lithium ions.